It is known in the areas of Ellipsometry, Polarimetry and Reflectometry or the like, to acquire a data set, (e.g. intensity, Ellipsometric PSI, Ellipsometric DELTA over Time), which characterizes a sample, by causing a beam of electromagnetic radiation to interact with the sample, and determining changes in the beam caused by said interaction.
It is also known that the act of observing a sample can cause change to occur thereto. For instance, especially over a prolonged time needed to make a plurality of measurements, energy delivered to a sample by a beam of electromagnetic radiation impinging thereupon can catalyze reaction of the sample surface with said atmospheric components to the end that deposition of said atmospheric components occurs onto said sample. This can lead to a measurable change, (i.e. sample drift), of, for instance, measured film thickness on said sample surface over time.
It is also known that data acquisition systems such as ellipsometers and reflectometers can change, (i.e. systemic drift), during application thereof in monitoring a sample, leading to acquisition of data which falsely represents sample composition.
Known patents which address handling data sets are:    U.S. Pat. No. 7,151,605 to Herzinger et al. describes a method of replacing data points in a data set determined to be bad, while maintaining the remainder of the data set; and    U.S. Pat. No. 7,307,724 to Liphardt et al. describes a method reducing the effect of noise in a data set.
Another known patent, while not directly related to the handling of data sets is:    Patent to Johs et al., U.S. Pat. No. 6,034,777 which describes a method for compensating for the effects of the presence of polarization state affecting input/output, elements in an ellipsometer system.
Another reference identified is an EPO Application titled “Method and Apparatus for Measuring Thickness of Thin Films on Substrate”, No. EP 1 577 636 B1 by Dianippon Screen Mfg., published 21 Sep. 2005.
Need exists for methodology that allows compensating for sample and/or systemic drift during data acquisition.